A sensitive radioimmunoassay measuring serum medroxyprogesterone acetate (MPA) has been developed in order to measure and correlate serum MPA concentrations and ovarian function in women following im administration of deop-MPA (DMPA), employing goat anti-MPA-3-(O-carboxymethyl) oxime-bovine serum albumin and MPA-3-(O-carboxymethyl) imino-125I-iodohistamine. In the 3 women studied, im injection of 150 mg of DMPA yielded brief initial serum MPA concentrations ranging from 1.5 to 3 ng/ml for a few days. Serum MPA concentrations gradually declined and remained relatively constant at about 1 ng/ml for 2 to 3 months, declined gradually thereafter reaching 0.2 ng/ml during the 6th month and became undetectable (less than 0.02 ng/ml) about 7-1/2 to 9 months following administration. Serum estradiol remained at early to midfollicular phase levels for 4 to 6 months after DMPA injection and rose to preovulatory levels when serum MPA levels fell below 0.5 to 0.25 ng/ml. Ovulation, however, as evidenced by serum progesterone concentrations did not occur, apparently due to suppression of the LH peak by positive feedback inhibition. Prolonged inhibition of cyclic ovarian function following DMPA injection is caused by slow MPA absorption and persists until serum MPA levels have decreased below 0.1 ng/ml or become undetectable about 7 to 9 months after DMPA administration.
PIP: Serum medroxyprogesterone acetate (MPA) concentrations were measured by a newly developed, highly sensitive, radioimmunoassay technique, and ovarian function was evaluated in 3 women after a single im injection of MPA (150 mg). Initial MPA concentrations ranged from 1.5 to 3 ng/ml for the 1st few days, and then gradually declined to a relatively constant level of about 1 ng/ml for 2-3 months. During the 6th month, MPA concentrations had declined to about .2 ng/ml, and became undetectable between 7!-9 months. Serum estradiol levels remained at early or midfollicurlar phase values for 4-6 months following injection, and then increased to preovulatory values (.25-.5 ng/ml). However, ovulation did not occur as determined by serum progesterone concentrations. Prolonged suppression of ovarian function by depo-MPA is due to the slow release of MPA; from the injection site.